A volume density optical model

A simple, but accurate, formal volume density optical model is developed for volume rendering scattered data or scalar fields from the finite element method, as opposed to scanned data sets where material classification is involved. The model is suitable either for ray tracing or projection methods and allows maximum flexibility in setting color and opacity. An expression is derived for the light intensity along a ray in terms of six userspecified transfer functions, three for optical density and three for color. Closed form solutions under several different assumptions are presented including a new exact result for the case that the transfer functions vary piecewise linearly along a ray segment within a cell.